Touch Sensing Device and Method for Driving the Same

ABSTRACT

A touch sensing device includes a touch screen coupled with a display panel including data lines, gate lines crossing the data lines, and pixels arranged in a matrix form, and a touch sensing circuit which supplies a driving signal to lines of the touch screen and senses a touch input. The touch sensing circuit detects an optimum sensing time, in which changes in a voltage change of the gate lines are maintained within a previously determined allowable range, in a touch screen drive period in which data is not written to the pixels of the display panel. The touch sensing circuit supplies the driving signal to the lines of the touch screen only in the optimum sensing time of the touch screen drive period.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/400,940 filed on Jan. 6, 2017, which is a continuation of U.S. patentapplication Ser. No. 15/041,000 filed on Feb. 10, 2016, which is acontinuation of U.S. patent application Ser. No. 13/712,753 filed onDec. 12, 2012, which claims the benefit of Korean Patent App. No.10-2012-0056388 filed on May 25, 2012, the contents of which are allincorporated hereby by reference for all purposes as if fully set forthherein.

BACKGROUND OF THE INVENTION Field of the Invention

Embodiments of the invention relate to a touch sensing device coupledwith a display device and a method for driving the same.

Discussion of the Related Art

User interface (UI) is configured so that users are able to communicatewith various electronic devices and thus can easily and comfortablycontrol the electronic devices as they desire. Examples of the userinterface include a keypad, a keyboard, a mouse, an on-screen display(OSD), and a remote controller having an infrared communication functionor a radio frequency (RF) communication function. User interfacetechnologies have continuously evolved to increase user's sensibilityand handling convenience. The user interface has been recently developedto touch UI, voice recognition UI, 3D UI, etc., and the touch UI hasbeen basically installed in portable information devices. A touch screenis installed on a display panel of household appliances or the portableinformation devices, so as to implement the touch UI.

A capacitive touch screen has greater durability and definition than anexisting resistive touch screen and is able to carry out multi-touchrecognition and proximity-touch recognition. Hence, the capacitive touchscreen may be applied to various applications. Because the capacitivetouch screen is attached to the display panel or is embedded in thedisplay panel, the capacitive touch screen is electrically coupled withthe display panel. The display panel and the touch screen may betime-division driven in a display panel drive period and a touch screendrive period. Because a data voltage having a relatively large swingwidth is supplied to data lines of the display panel in the displaypanel drive period, a load of the display panel increases.

A current path between an output channel of a data driving circuit andthe data lines of the display panel is cut off during the touch screendrive period. Hence, the data lines are floated, and are in a highimpedance state or are held at DC voltage. Thus, the load of the displaypanel during the touch screen drive period is less than the load of thedisplay panel during the display panel drive period. During the displaypanel drive period, a gate pulse (or scan pulse), which swings between agate high voltage and a gate low voltage, is supplied to gate lines (orscan lines) of the display panel. During the touch screen drive period,the gate lines of the display panel may be held at the DC voltage, forexample, the gate low voltage.

The gate low voltage supplied to the gate lines of the display panelchanges because of a load difference between the display panel driveperiod and the touch screen drive period. For example, when the gate lowvoltage supplied to the gate lines of the display panel is −10V in thetouch screen drive period, the gate low voltage of the gate lines ismeasured to almost −10V because the load of the display panel is smallin the touch screen drive period. On the other hand, when the gate lowvoltage supplied to the gate lines of the display panel is −10V in thedisplay panel drive period, the gate low voltage measured in the gatelines increases to almost −8V because of the large load of the displaypanel.

The gate low voltage supplied to the gate lines of the display panel maygreatly change in a period, which changes from the display panel driveperiod to the touch screen drive period and vice versa, because of theload difference between the display panel drive period and the touchscreen drive period. When the gate low voltage greatly changes, a noiseof a voltage sensed from the touch screen greatly changes due toelectrical coupling between the touch screen and the display panel. Thenoise reduces the sensing sensitivity of the touch screen.

SUMMARY OF THE INVENTION

Embodiments of the invention provide a touch sensing device and a methodfor driving the same capable of reducing a noise of a touch screen.

In one aspect, there is a touch sensing device including a touch screencoupled with a display panel including data lines, gate lines crossingthe data lines, and pixels arranged in a matrix form, and a touchsensing circuit configured to supply a driving signal to lines of thetouch screen and sense a touch input.

The touch sensing circuit detects an optimum sensing time, in which avoltage change of the gate lines are maintained within a previouslydetermined allowable range, in a touch screen drive period in which datais not written to the pixels of the display panel. The touch sensingcircuit supplies the driving signal to the lines of the touch screenonly in the optimum sensing time of the touch screen drive period.

The touch sensing device further includes a controller configured totime-divide one frame period into a display panel drive period and thetouch screen drive period and control a display panel driving circuitand the touch sensing circuit.

The display panel driving circuit writes data to the pixels of thedisplay panel during the display panel drive period.

The touch sensing circuit counts sync signals received from thecontroller and detects the optimum sensing time based on a count value.Alternatively, the touch sensing circuit detects the voltage of the gatelines and detects the optimum sensing time based on changes in thedetected voltage.

The optimum sensing time ranges from a time, at which a first transitionperiod has passed from a start time point of the touch screen driveperiod, to a time which is advanced from an end time point of the touchscreen drive period by a second transition period.

A ripple of a voltage measured in the gate lines during the optimumsensing time is less than a ripple of a voltage measured in the gatelines during the first and second transition periods.

In another aspect, there is a method for driving a touch sensing deviceincluding a touch screen coupled with a display panel including datalines, gate lines crossing the data lines, and pixels arranged in amatrix form, the method including setting a touch screen drive period,in which data is not written to the pixels of the display panel,detecting an optimum sensing time, in which a voltage change of the gatelines are maintained within a previously determined allowable range, inthe touch screen drive period, and supplying a driving signal to linesof the touch screen only in the optimum sensing time of the touch screendrive period.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIGS. 1 to 3 illustrate various combinations of a touch screen and adisplay panel according to an example embodiment of the invention;

FIG. 4 is a block diagram of a display device according to an exampleembodiment of the invention;

FIG. 5 is an equivalent circuit diagram of a liquid crystal cell;

FIG. 6 is a waveform diagram of a vertical sync signal showing atime-division driving method of a display panel and a touch screen;

FIG. 7 is a plane view showing a line structure of a mutual capacitivetouch screen which is embedded in a display panel in an in-cell type;

FIG. 8 is a waveform diagram showing an operation of a display device,in which the mutual capacitive touch screen shown in FIG. 7 is embedded;

FIG. 9 is a plane view showing a line structure of a self-capacitivetouch screen which is embedded in a display panel in an in-cell type;

FIG. 10 is a waveform diagram showing a driving signal for sensing theself-capacitive touch screen shown in FIG. 9;

FIG. 11 illustrates a multiplexer installed between a touch sensingcircuit and sensing lines;

FIG. 12 is an equivalent circuit diagram of a self-capacitive touchscreen;

FIG. 13 is a waveform diagram showing a sensing principle of a touchinput in a self-capacitive touch screen;

FIG. 14 is a block diagram of a touch sensing circuit according to afirst embodiment of the invention;

FIG. 15 is a block diagram of a touch sensing circuit according to asecond embodiment of the invention;

FIG. 16 is a timing diagram of a section showing a small change in agate low voltage;

FIG. 17A is a waveform diagram showing in detail a portion “A” of FIG.16; and

FIG. 17B is a waveform diagram showing in detail a portion “B” of FIG.16.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to embodiments of the invention,examples of which are illustrated in the accompanying drawings. Whereverpossible, the same reference numbers will be used throughout thedrawings to refer to the same or like parts. It will be paid attentionthat detailed description of known arts will be omitted if it isdetermined that the arts can mislead the embodiments of the invention.

A display device according to an example embodiment of the invention maybe implemented based on a flat panel display, such as a liquid crystaldisplay (LCD), a field emission display (FED), a plasma display panel(PDP), an organic light emitting diode (OLED) display, and anelectrophoresis display (EPD). In the following description, theembodiment of the invention will be described using the liquid crystaldisplay as an example of the flat panel display. Other flat paneldisplays may be used.

A touch screen TSP may be installed in the display device according tothe embodiment of the invention using methods shown in FIGS. 1 to 3. Asshown in FIG. 1, the touch screen TSP may be attached on an upperpolarizing film POL1 of a display panel. Alternatively, as shown in FIG.2, the touch screen TSP may be formed between the upper polarizing filmPOL1 and an upper substrate GLS1. Alternatively, as shown in FIG. 3,capacitive touch sensors of the touch screen TSP may be embedded in apixel array of the display panel. In FIGS. 1 to 3, ‘PIX’ denotes a pixelelectrode of a pixel, ‘GLS2’ denotes a lower substrate, and POL2′denotes a lower polarizing film.

The touch screen TSP may be implemented as a capacitive touch screenwhich senses a touch (or proximity) input through a plurality ofcapacitive sensors. The capacitive touch screen is classified into aself-capacitive touch screen and a mutual capacitive touch screen. Theself-capacitive touch screen is formed along a conductor line of asingle-layered structure formed in one direction. The mutual capacitivetouch screen is formed between two conductor lines which are orthogonalto each other.

As shown in FIGS. 4 and 5, the display device according to theembodiment of the invention includes a display panel 10, a display paneldriving circuit, a timing controller 22, a touch sensing circuit 100,etc. All components of the display device are operatively coupled andconfigured.

The display panel 10 includes a lower substrate, an upper substrate, anda liquid crystal layer formed between the lower substrate and the uppersubstrate. The upper and lower substrates may be manufactured usingglass, plastic, film, etc. A pixel array formed on the lower substrateof the display panel 10 includes a plurality of data lines 11, aplurality of gate lines (or scan lines) 12 orthogonal to the data lines11, and a plurality of pixels arranged in a matrix form. The pixel arrayfurther includes a plurality of thin film transistors (TFTs) formed atcrossings of the data lines 11 and the gate lines 12, a plurality ofpixel electrodes 1 for charging the pixels to a data voltage, aplurality of storage capacitors, each of which is connected to the pixelelectrode 1 and holds a voltage of the pixel, etc.

The pixels of the display panel 10 are arranged in a matrix form definedby the data lines 11 and the gate lines 12. A liquid crystal cell ofeach pixel is driven by an electric field generated depending on avoltage difference between the data voltage supplied to the pixelelectrode 1 and a common voltage supplied to a common electrode 2,thereby adjusting an amount of incident light transmitted by the liquidcrystal cell. Each of the TFTs is turned on in response to a gate pulse(or a scan pulse) from the gate line 11, thereby supplying the datavoltage from the data line 11 to the pixel electrode 1 of the liquidcrystal cell. The common electrode 2 may be formed on the lowersubstrate or the upper substrate of the display panel 10.

The upper substrate of the display panel 10 may include black matrixes,color filters, etc. Polarizing films are respectively attached to theupper and lower substrates of the display panel 10. Alignment layers forsetting a pre-tilt angle of liquid crystals are respectively formed onthe inner surfaces contacting the liquid crystals in the upper and lowersubstrates of the display panel 10. A column spacer may be formedbetween the upper and lower substrates of the display panel 10 to keep acell gap of the liquid crystal cells constant.

The display panel 10 may be implemented in any known mode including atwisted nematic (TN) mode, a vertical alignment (VA) mode, an in-planeswitching (IPS) mode, a fringe field switching (FFS) mode, etc. Abacklight unit may be disposed in a back space of the display panel 10.The backlight unit may be configured as one of an edge type backlightunit and a direct type backlight unit to provide light to the displaypanel 10.

The display panel driving circuit writes data of an input image to thepixels of the display panel 10 using a data driving circuit 24 and gatedriving circuits 26 and 30.

The data driving circuit 24 converts digital video data RGB receivedfrom the timing controller 22 into positive and negative analog gammacompensation voltages to generate the data voltage. The data drivingcircuit 24 then supplies the data voltage to the data lines 11 andinverts a polarity of the data voltage under the control of the timingcontroller 22.

The gate driving circuits 26 and 30 sequentially supply the gate pulsesynchronized with the data voltage to the gate lines 12 and select linesof the display panel 10 to which the data voltage will be applied. Thegate driving circuits 26 and 30 include a level shifter 26 and a shiftregister 30. The shift register 30 may be directly formed on thesubstrate of the display panel 10 with the development of a gate inpanel (GIP) process technology.

The level shifter 26 may be formed on a printed circuit board (PCB) 20electrically connected to the lower substrate of the display panel 10.The level shifter 26 outputs a start pulse VST and clock signals CLK,which swing between a gate high voltage VGH and a gate low voltage VGL,under the control of the timing controller 22. The gate high voltage VGHis set to be greater than a threshold voltage of the TFT included in thepixel array of the display panel 10. The gate low voltage VGL is set tobe less than the threshold voltage of the TFT. The level shifter 26outputs the start pulse VST and the clock signals CLK, which swingbetween the gate high voltage VGH and the gate low voltage VGL, inresponse to a start pulse ST, a first clock GCLK, and a second clockMCLK which are received from the timing controller 22. Phases of theclock signals CLK output from the level shifter 26 are sequentiallyshifted and are transmitted to the shift register 30 on the displaypanel 10.

The shift register 30 is formed at an edge of the lower substrate of thedisplay panel 10, on which the pixel array is formed, so that it isconnected to the gate lines 12 of the pixel array. The shift register 30includes a plurality of cascade-connected stages. The shift register 30starts to operate in response to the start pulse VST received from thelevel shifter 26 and shifts its output in response to the clock signalsCLK received from the level shifter 26. The shift register 30sequentially supplies the gate pulse to the gate lines 12 of the displaypanel 10.

The timing controller 22 supplies the digital video data RGB receivedfrom an external host system to integrated circuits (ICs) of the datadriving circuit 24. The timing controller 22 receives timing signals,such as a vertical sync signal Vsync, a horizontal sync signal Hsync, adata enable DE, and a clock, from the host system and generates timingcontrol signals for controlling operation timings of the data drivingcircuit 24 and the gate driving circuits 26 and 30. The timingcontroller 22 or the host system generates a sync signal SYNC forcontrolling operation timings of the display panel driving circuit andthe touch sensing circuit 100.

The touch sensing circuit 100 applies a driving signal to linesconnected to the capacitive sensors of the touch screen TSP and countschanges in voltage of the driving signal before and after a touchoperation or a delay time of a rising or falling edge of the drivingsignal, thereby sensing changes in the capacitance of the touch screenTSP before and after a touch (or proximity) input. The touch sensingcircuit 100 converts the voltage received from the capacitive sensors ofthe touch screen TSP into digital data to generate touch raw data. Thetouch sensing circuit 100 performs a previously determined touchrecognition algorithm and analyzes the touch raw data, thereby detectingthe touch (or proximity) input. The touch sensing circuit 100 transmitstouch report data including coordinates of a position of the touch (orproximity) input to the host system.

The host system may be implemented as one of a navigation system, aset-top box, a DVD player, a Blu-ray player, a personal computer (PC), ahome theater system, a broadcasting receiver, and a phone system. Thehost system converts digital video data of the input image into a dataformat suitable for a resolution of the display panel 10 using a scalerand transmits the converted data and the timing signals to the timingcontroller 22. The host system runs an application associated with thetouch (or proximity) input in response to the touch report data receivedfrom the touch sensing circuit 100.

The display panel 10 and the touch screen TSP may be time-divisiondriven using a method illustrated in FIG. 6. As shown in FIG. 6, oneframe period may be time-divided into a display panel drive period T1and a touch screen drive period T2.

In FIG. 6, ‘Vsync’ is a first vertical sync signal input to the timingcontroller 22, and ‘SYNC’ is a second vertical sync signal input to thetouch sensing circuit 100. The timing controller 22 may modulate thefirst vertical sync signal Vsync received from the host system andgenerate the second vertical sync signal SYNC, so as to define thedisplay panel drive period T1 and the touch screen drive period T2 inone frame period. In another embodiment, the host system may generatethe second vertical sync signal SYNC shown in FIG. 6, and the timingcontroller 22 may control the display panel drive period T1 and thetouch screen drive period T2 in response to the second vertical syncsignal SYNC received from the host system. Thus, in the embodiment ofthe invention, a controller, which time-divides one frame period intothe display panel drive period T1 and the touch screen drive period T2and controls the operation timings of the display panel driving circuitand the touch sensing circuit 100, may one of the timing controller 22and the host system.

A low logic level period of the second vertical sync signal SYNC may bedefined as the display panel drive period T1, and a high logic levelperiod of the second vertical sync signal SYNC may be defined as thetouch screen drive period T2. However, the embodiment of the inventionis not limited thereto. For example, the high logic level period of thesecond vertical sync signal SYNC may be defined as the display paneldrive period T1, and the low logic level period of the second verticalsync signal SYNC may be defined as the touch screen drive period T2.

During the display panel drive period T1, the display panel drivingcircuit is driven, and the touch sensing circuit 100 is not driven. Morespecifically, during the display panel drive period T1, the data drivingcircuit 24 supplies the data voltage to the data lines 11, and the gatedriving circuits 26 and 30 sequentially supply the gate pulsesynchronized with the data voltage to the gate lines 12. The touchsensing circuit 100 does not supply the driving signal to the lines ofthe touch screen TSP during the display panel drive period T1. Duringthe touch screen drive period T2, the display panel driving circuit isnot driven, and the touch sensing circuit 100 is driven. The touchsensing circuit 100 detects an optimum sensing time Tss (refer to FIGS.16 to 17B) in the touch screen drive period T2 and applies the drivingsignal to the lines of the touch screen TSP only during the optimumsensing time Tss. A voltage change of the gate lines 12 of the displaypanel 10 are maintained within a previously determined allowable rangeAr2 (refer to FIGS. 17A and 17B). Thus, the touch sensing circuit 100senses a change in a capacitive voltage of the touch screen TSP in theoptimum sensing time Tss, in which a noise from the display panel 10 hasa minimum value, thereby increasing the sensing sensitivity of the touch(or proximity) input. The lines of the touch screen TSP may be Tx lines(refer to FIG. 7) connected to mutual capacitive sensors shown in FIGS.1 to 3 or sensing lines S1 to Sn (refer to FIG. 9) connected toself-capacitive sensors.

The touch screen TSP shown in FIG. 3, in which capacitances are embeddedin the display panel 10 in an in-cell type, is more sensitively affectedby changes in the load of the display panel 10 than the touch screen TSPshown in FIGS. 1 and 2. A line structure and a driving method of anin-cell type touch screen are described below.

FIGS. 7 and 8 illustrate a line structure and a driving method of amutual capacitive touch screen. More specifically, FIG. 7 is a planeview showing a line structure of the mutual capacitive touch screen byenlarging the mutual capacitive touch screen, which is embedded in thedisplay panel in the in-cell type, and a portion of the display panel.FIG. 8 is a waveform diagram showing an operation of the display device,in which the mutual capacitive touch screen shown in FIG. 7 is embedded.

As shown in FIGS. 7 and 8, the mutual capacitive touch screen TSPincludes Tx lines and Rx lines R1 and R2 orthogonal to the Tx lines. Amutual capacitance is formed at each of crossings of the Tx lines andthe Rx lines R1 and R2.

Each of the Tx lines includes a plurality of transparent conductivepatterns which are connected to each other along a transverse direction(or a horizontal direction) of the display panel 10 through linkpatterns L11 to L22. For example, a first Tx line includes a pluralityof transparent conductive patterns T11 to T13 which are connected toeach other along the transverse direction of the display panel 10through the link patterns L11 and L12. A second Tx line includes aplurality of transparent conductive patterns T21 to T23 which areconnected to each other along the transverse direction through the linkpatterns L21 and L22. Each of the transparent conductive patterns T11 toT23 is patterned so that its size is greater than the size of thepixels, and thus overlaps the plurality of pixels. Each of thetransparent conductive patterns T11 to T23 overlaps the pixel electrodeswith an insulating layer interposed therebetween, and may be formed of atransparent conductive material, for example, indium tin oxide (ITO).Other materials may be used. The link patterns L11 to L22 electricallyconnect the transparent conductive patterns T11 to T23, which areadjacent to each other in the transverse direction, to one anotheracross the Rx lines R1 and R2. The link patterns L11 to L22 may overlapthe Rx lines R1 and R2 with an insulating layer interposed therebetween.The link patterns L11 to L22 may be formed of a metal with the highelectrical conductivity, for example, aluminum (Al), aluminum neodymium(AlNd), molybdenum (Mo), chromium (Cr), copper (Cu), and silver (Ag), ora transparent conductive material. Other materials may be used. Thetransparent conductive patterns divided from the common electrode 2 maybe used as Tx electrodes, to which the driving signal is applied.

The Rx lines R1 and R2 extend in a longitudinal direction (or a verticaldirection) of the display panel 10, so that they are orthogonal to theTx lines. The Rx lines R1 and R2 may be formed of a transparentconductive material, for example, indium tin oxide (ITO). Othermaterials may be used. Each of the Rx lines R1 and R2 may overlap theplurality of pixels (not shown). The Rx lines R1 and R2 may be formed onthe upper substrate or the lower substrate of the display panel 10. Forexample, Rx electrodes may be formed on a front surface or a backsurface of the upper substrate or the lower substrate of the displaypanel 10. In the in-cell type touch screen TSP shown in FIG. 3, the datalines of the pixel array may be used as the Rx electrodes, or the pixelarray may include separate lines to be used as the Rx electrodes.

A common voltage source supplies a common voltage Vcom to the Tx linesT11 to T23 and L11 to L22 during the display panel drive period T1.Thus, the Tx lines T11 to T23 and L11 to L22 operate as the commonelectrode 2 during the display panel drive period T1.

The touch sensing circuit 100 is connected to the Tx lines T11 to T23and L11 to L22 and the Rx lines R1 and R2. The touch sensing circuit 100is disabled during the display panel drive period T1 and is enabledduring the touch screen drive period T2. Hence, only during the touchscreen drive period T2, the touch sensing circuit 100 sequentiallysupplies the driving signal to the Tx lines T11 to T23 and L11 to L22and receives the voltages of the mutual capacitances through the Rxlines R1 and R2. The driving signal swings between a driving voltageVdry and a reference voltage Vref. In FIGS. 7 and 8, ‘D1, D2, D3 . . . ’denote the data lines of the display panel 10, and ‘G1, G2, G3 . . . ’denote the gate lines of the display panel 10.

The touch sensing circuit 100 samples the voltages of the mutualcapacitances received through the Rx lines R1 and R2 and accumulates thesampled voltages to a capacitor of an integrator. The touch sensingcircuit 100 converts a voltage charged to the capacitor of theintegrator into digital data. The touch sensing circuit 100 compares thedigital data with a previously determined threshold voltage and decidesdigital data equal to or greater than the threshold voltage as mutualcapacitance data of a touch (or proximity) input position.

FIG. 9 is a plane view showing a line structure of a self-capacitivetouch screen which is embedded in the display panel in the in-cell type.FIG. 10 is a waveform diagram showing a driving signal for sensing theself-capacitive touch screen shown in FIG. 9.

As shown in FIGS. 9 and 10, the self-capacitive touch screen TSPincludes a plurality of transparent conductive patterns COM1 to COMn.Each of the transparent conductive patterns COM1 to COMn is patterned sothat its size is greater than the size of the pixels, and thus overlapsthe plurality of pixels. The transparent conductive patterns COM1 toCOMn may be formed of a transparent conductive material. Other materialsmay be used. Each of the transparent conductive patterns COM1 to COMn isconnected to a self-capacitance and is used as an electrode of theself-capacitance during the touch screen drive period T2.

The touch sensing circuit 100 may be connected to the transparentconductive patterns COM1 to COMn through sensing lines S1 to Sn on aone-to-one basis. The common voltage source (not shown) supplies thecommon voltage Vcom to the transparent conductive patterns COM1 to COMnthrough the sensing lines S1 to Sn during the display panel drive periodT1. Thus, the transparent conductive patterns COM1 to COMn operate asthe common electrode during the display panel drive period T1.

The touch sensing circuit 100 is disabled during the display panel driveperiod T1 and is enabled during the touch screen drive period T2. Hence,the touch sensing circuit 100 simultaneously supplies the driving signalshown in FIG. 10 to the sensing lines S1 to Sn only during the touchscreen drive period T2. Although the display panel drive period T1 isnot shown in FIG. 10, an operation of the display panel drive period T1is substantially the same as FIG. 8.

As shown in FIG. 11, a multiplexer 102 may be installed between thetouch sensing circuit 100 and the sensing lines S1 to Sn, so as toreduce the number of input/output pins of the touch sensing circuit 100in the self-capacitive touch screen TSP. When the multiplexer 102 isimplemented as 1:N multiplexer, where N is a positive integer equal toor greater than 2 and less than n, n/N input/output pins of the touchsensing circuit 100, to which the driving signal is output, areconnected to input terminals of the multiplexer 102. The n outputterminals of the multiplexer 102 are respectively connected to thesensing lines S1 to Sn. Thus, the embodiment of the invention may reducethe number of input/output pins of the touch sensing circuit 100 by 1/Nusing the multiplexer 102.

When the sensing lines S1 to Sn are divided into three groups, themultiplexer 102 connects n/3 input/output pins P1 to Pn/3 of the touchsensing circuit 100 to the sensing lines of a first group andsimultaneously supplies the driving signal to capacitive sensorsconnected to the sensing lines of the first group. Subsequently, themultiplexer 102 connects the n/3 input/output pins P1 to Pn/3 to thesensing lines of a second group and simultaneously supplies the drivingsignal to capacitive sensors connected to the sensing lines of thesecond group. Subsequently, the multiplexer 102 connects the n/3input/output pins P1 to Pn/3 to the sensing lines of a third group andsimultaneously supplies the driving signal to capacitive sensorsconnected to the sensing lines of the third group. Thus, the touchsensing circuit 100 may supply the driving signal to the n transparentconductive patterns COM1 to COMn through the n/3 input/output pins P1 toPn/3 using the multiplexer 102.

FIG. 12 is an equivalent circuit diagram of the self-capacitive touchscreen. FIG. 13 is a waveform diagram showing a sensing principle of atouch input in the self-capacitive touch screen.

As shown in FIGS. 12 and 13, the self-capacitive touch screen TSPincludes a resistor R and capacitors Cg, Cd, and Co. The resistor Rincludes a line resistance and a parasitic resistance of theself-capacitive touch screen TSP and the display panel 10. The capacitorCg is positioned between the lines of the self-capacitive touch screenTSP and the gate lines 12, and the capacitor Cd is positioned betweenthe lines of the self-capacitive touch screen TSP and the data lines 11.The capacitor Co is positioned between the lines of the self-capacitivetouch screen TSP and other components of the display panel 10 except thedata lines 11 and the gate lines 12.

When a driving signal Vo is applied to the lines of the self-capacitivetouch screen TSP, a rising edge and a falling edge of the driving signalVo are delayed by an RC delay value determined by the resistor R and thecapacitors Cg, Cd, and Co shown in FIG. 12. When a user touches theself-capacitive touch screen TSP with a conductor or his or her finger,the capacitance of the self-capacitive touch screen TSP increases by‘Cf’ shown in FIG. 13, and the RC delay further increases. For example,in FIG. 13, the solid line indicates the falling edge of the drivingsignal Vo when there is no touch input, and the dotted line indicatesthe falling edge of the driving signal Vo when the touch input isperformed. The touch sensing circuit 100 compares a voltage of at leastone of the rising edge and the falling edge of the driving signal Vowith a previously determined reference voltage Vx. The touch sensingcircuit 100 counts a time required to reach the voltage of at least oneof the rising edge and the falling edge of the driving signal Vo to thereference voltage Vx. Reference time information, which is required toreach the voltage of at least one of the rising edge and the fallingedge of the driving signal Vo to the reference voltage Vx when there isno touch input, is previously stored in the touch sensing circuit 100.When a difference Δt between a time measured in real time by a counterand the previously known reference time information is equal to orgreater than a previously determined threshold value, the touch sensingcircuit 100 decides a currently sensed self-capacitance as the touch (orproximity) input.

The gate pulse, which swings between the gate high voltage VGH and thegate low voltage VGL, is applied to the gate lines 12 of the displaypanel 10 during the display panel drive period T1. Subsequently, thegate low voltage VGL is continuously applied to the gate lines 12 of thedisplay panel 10 during the touch screen drive period T2. The gate lowvoltage VGL applied to the gate lines 12 of the display panel 10 maygreatly change in a period, which changes from the display panel driveperiod T1 to the touch screen drive period T2 and vice versa, because ofthe load difference between the display panel drive period T1 and thetouch screen drive period T2. The change of the gate low voltage VGL andan increase in a noise of the sensing voltage of the touch screen TSPresulting from the change of the gate low voltage VGL are proportionalto a magnitude of a ripple of the gate low voltage VGL which changesdepending on the load change of the display panel 10. As shown in FIGS.16 to 17B, the embodiment of the invention detects the change of thegate low voltage VGL in the touch screen drive period T2 and applies thedriving signal to the lines of the touch screen TSP only in a sensingsection Tss, in which the magnitude of the ripple of the gate lowvoltage VGL decreases, thereby sensing changes in the capacitance of thetouch screen TSP. The sensing section Tss exists in the touch screendrive period T2. The sensing section Tss starts at a time which is laterthan a start time point of the touch screen drive period T2 by a timeTd1, and ends at a time which is earlier than an end time point of thetouch screen drive period T2 by a time Td2.

The touch sensing circuit 100 may detect the sensing section Tss showingthe small change in the voltage of the gate line using various methods.FIGS. 14 and 15 illustrate examples of the touch sensing circuit 100having a detection function of the sensing section Tss.

FIG. 14 is a block diagram of the touch sensing circuit 100 according toa first embodiment of the invention.

As shown in FIG. 14, the touch sensing circuit 100 includes a counter104, a sensing section detector 106, a driving signal generator 108, anda sensing unit 110.

The counter 104 counts the sync signal SYNC using the clock signals fromthe start time point of the touch screen drive period T2 and initializesa count value CNT in each frame period. The clock signal may be a clocksignal received through the timing controller 22 or a clock signalreceived from an oscillator connected to the touch sensing circuit 100.

The present inventors repeatedly conducted an experiment and found anoptimum sensing time, in which the changes of the gate low voltage VGLare within the previously determined allowable range Ar2 (refer to FIGS.17A and 17B), in the touch screen drive period T2. The present inventorsmay previously store informations T2, Td1, and Td2 (refer to FIGS. 17Aand 17B) related to the optimum sensing time in a memory of the sensingsection detector 106. The sensing section detector 106 compares thecount value CNT received from the counter 104 with the time Td1 anddecides a time required to reach the count value CNT from the time Td1to a time T2−(Td1+Td2) as the optimum sensing time. The sensing sectiondetector 106 generates an output (Tss of FIG. 6) generated at a specificlogic value during the optimum sensing time.

The driving signal generator 108 generates driving signals only duringthe sensing section Tss in response to the output of the sensing sectiondetector 106 and supplies the driving signals to the lines of the touchscreen TSP. The sensing unit 110 senses the changes in the capacitanceof the touch screen TSP in synchronization with the driving signals andgenerates touch raw data Txy based on the sensing result.

FIG. 15 is a block diagram of the touch sensing circuit 100 according toa second embodiment of the invention.

As shown in FIG. 15, the touch sensing circuit 100 includes a voltagedetector 112, a sensing section detector 114, a driving signal generator108, and a sensing unit 110.

The voltage detector 112 measures the voltage of the gate line 12 duringthe touch screen drive period T2.

The present inventors repeatedly conducted an experiment and previouslystored the voltage of the gate line 12 measured in an optimum sensingtime of the touch screen drive period T2, in which a noise is slightlygenerated in the touch screen TSP, in a memory of the sensing sectiondetector 114 as a reference value. The sensing section detector 114compares the voltage of the gate line 12 received from the voltagedetector 112 with the previously stored reference value and decides aperiod, in which a difference is within the previously determinedallowable range Ar2 (refer to FIGS. 17A and 17B), as an optimum sensingtime. The sensing section detector 114 generates an output (Tss of FIG.6) generated at a specific logic value during the optimum sensing time.

The driving signal generator 108 generates driving signals only duringthe sensing section Tss in response to the output of the sensing sectiondetector 114 and supplies the driving signals to the lines of the touchscreen TSP. The sensing unit 110 senses the changes in the capacitanceof the touch screen TSP in synchronization with the driving signals andgenerates touch raw data Txy based on the sensing result.

FIG. 16 is a timing diagram of a section showing a small change in thegate low voltage. FIG. 17A is a waveform diagram showing in detail aportion “A” of FIG. 16. FIG. 17B is a waveform diagram showing in detaila portion “B” of FIG. 16.

As shown in FIGS. 16 to 17B, the gate low voltage VGL, which is the DCvoltage, is applied to the gate lines 12 during the touch screen driveperiod T2.

During a transition period Td1 from the display panel drive period T1 tothe touch screen drive period T2, the load of the display panel 10 issharply reduced. On the contrary, during a transition period Td2 fromthe touch screen drive period T2 to the display panel drive period T1,the load of the display panel 10 is sharply increased. Thus, when about−10V is applied to the gate lines 12 during the touch screen driveperiod T2, the gate low voltage VGL measured in the gate lines 12 duringthe first and second transition periods Td1 and Td2 greatly changesbetween about −10V and a ground level voltage GND and includes a highripple Ar1. The ripple Ar1 of the voltage measured in the gate lines 12during the first and second transition periods Td1 and Td2 is greaterthan a ripple Ar2 of the voltage measured in the gate lines 12 duringthe sensing section Tss.

On the other hand, the load of the display panel 10 hardly changesduring the sensing section Tss ranging from a time, at which the firsttransition period Td1 has passed from a start time point of the touchscreen drive period T2, to a time, which is advanced from an end timepoint of the touch screen drive period T2 by the second transitionperiod Td2. Because of this, the voltage measured in the gate lines 12during the sensing section Tss changes around about −8V with the smallripple Ar2 and thus is measured as a current voltage which hardlychanges. The ripple Ar2 of the voltage measured in the gate lines 12during the sensing section Tss is much less than the ripple Ar1 of thevoltage measured in the gate lines 12 during the first and secondtransition periods Td1 and Td2. Thus, the touch sensing circuit 100applies driving signals SS to the lines of the touch screen TSP onlyduring the sensing section Tss of the touch screen drive period T2, inwhich the voltage of the gate lines 12 hardly changes, thereby sensingchanges in the capacitance of the touch screen TSP.

The touch screen according to the embodiment of the invention is notlimited to the in-cell type touch screen. For example, the touch sensingcircuit 100 shown in FIGS. 14 to 17B and the method for driving the samemay be applied to the various types of touch screens shown in FIGS. 1 to3.

As described above, the embodiment of the invention detects the optimumsensing time, in which the changes in the voltage of the gate lines arewithin the previously determined allowable range, in the touch screendrive period, in which data is not written to the pixels of the displaypanel, and supplies the driving signals to the lines of the touch screenonly in the optimum sensing time. As a result, the embodiment of theinvention may reduce the noise of the voltage sensed from the touchscreen resulting from the changes in the voltage of the gate lines ofthe display panel and increase the sensing sensitivity of the touchscreen.

Although embodiments have been described with reference to a number ofillustrative embodiments thereof, it should be understood that numerousother modifications and embodiments can be devised by those skilled inthe art that will fall within the scope of the principles of thisdisclosure. More particularly, various variations and modifications arepossible in the component parts and/or arrangements of the subjectcombination arrangement within the scope of the disclosure, the drawingsand the appended claims. In addition to variations and modifications inthe component parts and/or arrangements, alternative uses will also beapparent to those skilled in the art.

What is claimed is:
 1. A touch sensing display device comprising: adisplay panel including data lines, gate lines, sensing lines and touchelectrodes for sensing a touch and operated as common electrodes; and atouch sensing circuit configured to sense changes in capacitancecorresponding to the touch electrodes during a touch drive period,wherein: the touch electrodes include a first touch electrode and asecond touch electrode, the sensing lines include a first sensing lineand a second sensing line, the first sensing line is overlapped with thefirst touch electrode, the second sensing line is overlapped with thefirst touch electrode and the second touch electrode, the touch sensingcircuit is connected to the first touch electrode through the firstsensing line and is connected to the second touch electrode through thesecond sensing line, the touch drive period includes a first section, asensing section and a second section, the touch sensing circuit sensesthe first touch electrode and the second touch electrode to sensechanges in the capacitance corresponding to the first touch electrodeand the second touch electrode during the sensing section of the touchdrive period, the touch sensing circuit does not sense the first touchelectrode and the second touch electrode during the first section of thetouch drive period or during the second section of the touch driveperiod.
 2. The touch sensing display device of claim 1, furthercomprising; a display panel driving circuit configured to write data topixels of the display panel during a display drive period, and to notwrite data to the pixels of the display panel during the touch driveperiod.
 3. The touch sensing display device of claim 1, wherein avoltage of at least one of the gate lines is changed from a firstvoltage to a second voltage during the first section of the touch driveperiod or during the second section of the touch drive period.
 4. Thetouch sensing display device of claim 1, wherein the touch sensingcircuit supplies a touch driving signal to the first touch electrode andthe second touch electrode to sense changes in the capacitancecorresponding to the first touch electrode and the second touchelectrode during the sensing section.
 5. The touch sensing displaydevice of claim 1, wherein the touch sensing circuit is configured tooperate in a display mode or a touch mode depending on a control signal,wherein the first level of the control signal is indicative of thedisplay mode and the second level of the control signal is indicative ofthe touch mode.
 6. The touch sensing display device of claim 1, whereinthe sensing section of the touch drive period immediately follows thefirst section of the touch drive period.
 7. The touch sensing displaydevice of claim 1, wherein: a common voltage is supplied to the firsttouch electrode through the first sensing line and to the second touchelectrode through the second sensing line during a display drive period.8. The touch sensing display device of claim 7, wherein the commonvoltage is a direct current (DC) voltage.
 9. The touch sensing displaydevice of claim 1, wherein the first touch electrode is connected to thefirst sensing line but not connected to the second sensing line, and thesecond touch electrode is connected to the second sensing line but notconnected to the first sensing line.
 10. The touch sensing displaydevice of claim 1, wherein a size of the first touch electrode isgreater than a size of pixels of the display panel corresponding to thefirst touch electrode, and a size of the second touch electrode isgreater than a size of pixels of the display panel corresponding to thesecond touch electrode.
 11. A driver circuit for driving a touch sensingdisplay device including a display panel including data lines, gatelines, sensing lines and touch electrodes for sensing a touch andoperated as common electrodes, the touch electrodes include a firsttouch electrode and a second touch electrode, the sensing lines includea first sensing line and a second sensing line, the first sensing lineis overlapped with the first touch electrode, the second sensing line isoverlapped with the first touch electrode and the second touchelectrode, the driver circuit comprising: a touch sensing circuitconfigured to sense changes in capacitance corresponding to the touchelectrodes during a touch drive period; wherein the touch sensingcircuit is connected to the first touch electrode through the firstsensing line and is connected to the second touch electrode through thesecond sensing line, wherein the touch drive period includes a firstsection, a sensing section and a second section, wherein the touchsensing circuit senses the first touch electrode and the second touchelectrode to sense changes in the capacitance corresponding to the firsttouch electrode and the second touch electrode during the sensingsection of the touch drive period, wherein the touch sensing circuitdoes not sense the first touch electrode and the second touch electrodeduring the first section of the touch drive period or during the secondsection of the touch drive period.
 12. The driver circuit of claim 11,wherein data is written to pixels of the display panel during a displaydrive period, and wherein data is not written to pixels of the displaypanel during a touch drive period.
 13. The driver circuit of claim 11,wherein a voltage of at least one of the gate lines is changed from afirst voltage to a second voltage during the first section of the touchdrive period or during the second section of the touch drive period. 14.The driver circuit of claim 11, wherein the touch sensing circuitsupplies a touch driving signal to the first touch electrode and to thesecond touch electrode to sense changes in the capacitance correspondingto the first touch electrode and the second touch electrode during thesensing section.
 15. The driver circuit of claim 11, wherein the touchsensing circuit is configured to operate in a display mode or a touchmode depending on a control signal, wherein the first level of thecontrol signal is indicative of the display mode and the second level ofthe control signal is indicative of the touch mode.
 16. The drivercircuit of claim 11, wherein the sensing section of the touch driveperiod immediately follows the first section of the touch drive period.17. The driver circuit of claim 11, wherein a common voltage is suppliedto the first touch electrode through the first sensing line and to thesecond touch electrode through the second sensing line during a displaydrive period.
 18. The driver circuit of claim 17, wherein the commonvoltage is a direct current (DC) voltage.
 19. A method for driving atouch sensing display device including a display panel including datalines, gate lines, sensing lines and touch electrodes for sensing atouch and operated as common electrodes, the touch electrodes include afirst touch electrode and a second touch electrode, the sensing linesinclude a first sensing line and a second sensing line, the firstsensing line is overlapped with the first touch electrode, the secondsensing line is overlapped with the first touch electrode and the secondtouch electrode, and a touch sensing circuit configured to sense changesin capacitance corresponding to the touch electrodes during a touchdrive period, the touch drive period includes a first section, a sensingsection and a second section, the method comprising: sensing the firsttouch electrode and the second touch electrode to sense changes in thecapacitance corresponding to the first touch electrode and the secondtouch electrode during the sensing section of the touch drive period;and not sensing the first touch electrode and the second touch electrodeduring the first section of the touch drive period or during the secondsection of the touch drive period, wherein the touch sensing circuit isconnected to the first touch electrode through the first sensing lineand is connected to the second touch electrode through the secondsensing line.
 20. The method of claim 19, wherein the sensing section ofthe touch drive period immediately follows the first section of thetouch drive period.